Integrated circuits include many active devices in an integrated circuit substrate such as a semiconductor substrate. These active devices are generally isolated from one another. Accordingly, isolation structures and methods are widely used in integrated circuits. One important isolation structure and method is a trench isolation structure and method.
Conventional trench isolation structures are fabricated by forming a trench in an integrated circuit substrate and forming an isolation region of insulating material in the trench. Trench isolation structures and methods are described in U.S. Pat. 5,387,538 to Moslehi entitled "Method of Fabrication of Integrated Circuit Isolation Structure" and U.S. Pat. 5,447,884 to Fahey et al. entitled "Shallow Trench Isolation With Thin Nitride Liner".
In conventional trench isolation, defects may be caused due to stresses caused by the difference between the thermal expansion coefficients of the isolation material and the integrated circuit substrate. It has been found that the stresses may be concentrated at the corner of the trench, where the trench wall meets the trench floor. These stresses may impact the reliability and/or performance of the integrated circuit. In order to solve this problem, it has been proposed to round the corner of a trench region. See for example, the publication entitled "Micro Area Stress around Trench Structure" to Nadahara et al., Extended Abstracts of the 19.sup.th Conference on Solid State Devices and Materials, Tokyo, 1987, pp. 327-330. Notwithstanding this technique, there continues to be a need for trench isolation structures and methods that are capable of reducing stresses in the integrated circuit that are caused by the differences in thermal expansion coefficients between the integrated circuit substrate and the isolation region.